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Re: More /.{I->-1} craziness

  • To: mathgroup at smc.vnet.net
  • Subject: [mg106317] Re: More /.{I->-1} craziness
  • From: Richard Fateman <fateman at cs.berkeley.edu>
  • Date: Fri, 8 Jan 2010 04:15:33 -0500 (EST)
  • References: <200912300915.EAA17299@smc.vnet.net> <hhhmn8$o9t$1@smc.vnet.net> <hi42mv$nct$1@smc.vnet.net>

Noqsi wrote:

> 
> Mathematica has a tool that can do what you want here:
> 
> Reduce[a == Exp[I x] - Exp[-I x] && Exp[I x] == s, {a}, {x}]
> s != 0 && a == (-1 + s^2)/s
> 
> It's a bit fussier than perhaps you'd like, but that's mathematics for
> you ;-)
> 
Reduce is a really neat program in Mathematica, one that I especially 
admire since it was improved to work on more than polynomials.
Unfortunately, it won't work for I->-I, maybe because that is based on a 
decision involving constants represented differently from expressions 
that construct them.  (David Bailey already pointed this out.  Do people 
get instantaneous unfiltered feed from this newsgroup??)

but also..
Bill Rowe said ...
  "Again, the choice is either understand this behavior and live
   with it or find different software. There isn't any other
   productive choice."

Well, reporting something as a bug and hoping it will be fixed is 
another choice.
And writing a version of the facility that does the right thing is
another choice. (Any takers?)

Either of these could be "productive".

Are Mathematica design decisions sacred or something?

RJF


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